1. Field of the Invention
The present invention relates to a process for producing L-lysine by fermentation. L-lysine is one of the twenty naturally occurring essential amino acids. In addition to other uses, L-lysine is useful in livestock production. Since cereals, which are common livestock (e.g. broilers and pigs) feed, do not contain sufficient levels of the amino acid for the livestock's nutritional requirements it is necessary to supplement the feed with L-lysine. Thus it is necessary to develop an efficient method for L-lysine production.
2. Description of the Prior Art
In previously described processes for the microbial production of L-lysine by fermentation, specific lysine producing microorganisms have been isolated or derived from naturally occurring lysine producers. Most of these artificially selected mutants are derived from microorganisms belonging to the genus Brevibacterium or alternatively the genus Corynebacterium. In both of these genus, L-lysine production is achieved by potentiating the L-lysine biosynthesis system by a combination or sequential ligation of properties such as auxotrophy, sensitivity, analog resistance, etc. (Tosaka, Takinami in "Fermentation of Amino Acid", edited by Aida, Takinami, Chibata, Nakayama and Yamada, Gakkai Publishing Center, 1986, page 273 ff). These methods have limited ability to select organisms which produce L-lysine at increased levels. It is therefore a goal of the present invention to develop a method of producing microorganisms capable of producing increased levels of L-lysine by fermentation process.